Ultrasonic Surgical Tool System Including a Tip Capable of Simultaneous Longitudinal and Torsional Movement and a Console Capable of Applying a Drive Signal to the Tip so the Tip Engages in Substantially Torsional Oscillations

ABSTRACT

An ultrasonic tool system with a console and a tip that has a distal end that when vibrated vibrates both longitudinally and torsionally. The console applies a drive signal to the drivers that vibrate the tip that is at a longitudinal mechanical cancelation frequency. Consequently, when the tip is vibrated, at the distal end the longitudinal component of a first resonant mode of the tip cancel out the longitudinal component of the second resonant move of the tip so the distal end of the tip engages in vibrations that substantially torsional and only minimally longitudinal.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/004,453 filed Aug. 27, 2020, which is a continuation of U.S.patent application Ser. No. 16/062,969 filed Jun. 15, 2018, which is anational stage entry of International Patent App. No. PCT/US2016/066635filed Dec. 14, 2016, which claims priority to and all the benefits ofU.S. Provisional Patent App. No. 62/269,542 filed Dec. 18, 2015. Thecontents of the above applications are all hereby incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

This invention relates generally to an ultrasonically driven surgicalhandpiece. More particularly, this invention relates to anultrasonically driven handpiece that has plural modes of vibration and amethod of driving the handpiece so the tip head undergoes vibrationsthat are essentially torsion vibrations.

BACKGROUND OF THE INVENTION

Ultrasonic surgical instruments are useful surgical instruments forperforming certain medical and surgical procedures. Generally, anultrasonic surgical tool includes a handpiece that contains at least onepiezoelectric driver. A tip is mechanically coupled to the driver andextends forward from the housing or shell in which the driver isdisposed. The tip has a head. The head is provided with features, oftenteeth, dimensioned to accomplish a specific medical/surgical task. Anultrasonic tool system also includes a control console. The controlconsole supplies an AC drive signal to the driver. Upon the applicationof the drive signal to the driver, the driver cyclically expands andcontracts. The expansion/contraction of the driver induces acousticwaves that propagate along the tip. The acoustic waves induce the tip,especially the head, into a back and forth motion. When the tip somoves, the tip is considered to be vibrating. The vibrating head of thetip is applied against tissue to perform a specific surgical or medicaltask. For example, some tip heads are applied against hard tissue. Oneform of hard tissue is bone. When this type of tip head is vibrated, theback and forth vibrations of the tip teeth, saw, remove, the adjacenthard tissue. Still other tip heads are designed to be placed againstsoft tissue.

Some ultrasonic tools remove tissue by inducing cavitation in the tissueand surrounding fluid. Cavitation occurs as a result of the tip headmoving back and forth at or beyond a velocity that induces cavitation.Cavitation is the formation of small voids, cavities, in the tissue andsurrounding fluid adjacent the tip. These cavities are very small zonesof extremely low pressure. A pressure differential across the borderbetween these cavities and the cells forming the adjacent tissue. Owingto the relatively large magnitude of this pressure differential, thecell walls burst. The bursting of these cell walls, removes, ablates,the cells forming the tissue. Some tips are formed with teeth thatprotrude laterally outwardly from the side of the tip head.

Physically, many tips include an elongated shaft. The proximal or rearend of the shaft is connected to the handpiece. A head, the tip head, islocated at the distal end, the free end of the shaft. The head sometimesprojects outwardly from the adjacent portion of the shaft. The head ofan ultrasonic tip is often relatively small. Some heads have diametersof less than 1.0 cm. An ultrasonic tool removes tissue adjacent to wherethe head is applied. Owing to the relative small surface area of theirheads, ultrasonic handpieces have proven to be useful tools forprecisely removing both hard and soft tissue.

Other cutting implements used to selectively remove tissue are drillbits and burs. For a drill or bur to function, the implement is oftenrotated. Here, “rotation” is understood to mean repeating 360° movementaround the longitudinal through the implement. The mechanical force ofthis rotation can, when opposed to a resistive force of the tissue, cancause the implement to jump out of the path of the cut. Still anotherundesirable effect of this rotation is that when the shaft of theimplement invariably presses against tissue not intended for removal,the rotation can tear or otherwise damage the tissue. In contrast,neither the shaft nor the head of an ultrasonic tip rotates. This meanswhen this type of implement is used in a procedure, the likelihood thatthe tissue could be damages as a result of the rotation of the tip areessentially eliminated.

Most tips are designed so that when the drive signal is applied, the tiphead vibrates primarily in a single mode. Here the vibration mode isunderstood to be the path of travel along which the tip head travels.The majority of tips are designed to vibrate longitudinally. This meansthe heads move back and forth along an axis that is essentially in linewith the proximal-to-distal longitudinal axis along the tip.

A problem can arise when a tip vibrates longitudinally. This type oftip, as discussed above, is designed so that when a side face of the tiphead is applied against the tissue and vibrated, the teeth cut, resect,the tissue. Alternatively, or in combination with the cutting, the teethfoster cavitation that ablates the adjacent tissue. The problem occursbecause sometimes the distal end of the shaft of the tip can vibrate ata velocity that induces cavitation in the tissue against which this endof the head is pressed. This cavitation can cause the unwanted ablation,removal, of tissue not targeted for removal. The challenges posed byreducing this unwanted tissue removal are further complicated by thefact that this removal is occurring at the distal end of the tip head.This location is one that is typically concealed from the sight of thepractitioner. Consequently, it can be difficult for the practitioner todetermine if owing to the placement of the tip, if this unwanted tissueablation is occurring.

Some tips are available that vibrate in a mode other than a longitudinalmode. Some tips are designed so that their heads, when vibrated, engagein a torsional or rotation vibration. This means that that head, whenexcited into vibration, rotates around the tip longitudinal axis. Stillother tips are designed to flex. This rotation is back and forth motionaround an arc that subtends an angle less than 360°. This means thatwhen the tip is excited, the longitudinal axis of the tip bends back andforth. The tip head moves with the bending, the flexing of the tip.

A characteristic integral with an ultrasonic handpiece is the mechanicalresonant frequency of the handpiece. Here the handpiece is understood tomean both the drivers and the components of the handpiece coupled to thedrivers including the tip. The mechanical resonant frequency is thefrequency of these components at which, when the tip is vibrated at, thetip head undergoes vibratory motion of a peak range. For a tip thatvibrates longitudinally, the peak range is understood to be the largestback and forth distance. For a tip that vibrates torsionally orflexural, the maximum range is understood to be the largest arc in asingle phase of a vibratory cycle. Here peak range of motion isunderstood to be motion that is larger in magnitude than a motion thatwould occur if the drivers vibrate at a frequency slightly below orslightly above the resonant frequency.

Owing to their structure, some handpieces have plural mechanicalresonant modes. This means this type of handpiece has plural frequenciesat which, in comparison to adjacent frequencies, when the handpiece isvibrated, the tip head engages in a peak range of movement. Eachmechanical resonant frequency is associated with an individual one ofthe mechanical resonant modes.

The Applicant's PCT Pub. No. WO 2015/021216 A1/US Pat. Pub. No.10,016,209 B2, the contents of which are incorporated herein byreference, disclose a means for regulating the frequency of the drivesignal, so this signal is at a frequency that as closely as possiblematches the mechanical resonant frequency of the tip. Generally thisprocess is performed by determining whether or not the below Equation,Equation (11), in PCT Pub. No. WO 2015/021216 A1 tests true:

$\begin{matrix}{{{- {Re}}\left\{ \frac{\begin{matrix}{{COMPLEX}{ELECTRICAL}{CURRENT}{DUE}} \\{{TO}{THE}{CAPACITANCE}{OF}{THE}{DRIVERS}}\end{matrix}}{\begin{matrix}{{COMPLEX}{MECHANICAL}{EQUIVALENT}} \\{{OF}{CURRENT}{DUE}{TO}{THE}{MECHANICAL}} \\{{COMPONENTS}{OF}{THE}{HANDPiECE}}\end{matrix}} \right\}} = 0} & (1)\end{matrix}$

The frequency of the drive signal applied to the drivers functions as avariable of both the antecedent and the consequent of this ratio. PCTPub. No. WO 2015/021216 A1 teaches regulating the drive signal frequencyso the frequency is at a resonant frequency for a particular mechanicalresonant mode of the handpiece. Typically this resonant frequency is forthe mechanical resonant state of the handpiece which induces thevibrations of the largest peak range of movement of the tip head.

If the calculation to determine the above ratio yields a positiveresult, it is necessary to decrease the frequency of the drive signal soas to more closely match the resonant frequency of which results in themaximum desired vibrational movement. Typically the variables selectedto calculate the ratio are selected to determine the frequency of thedrive signal that will cause the tip to vibrate at the resonantfrequency of the resonant state where longitudinal mode and torsionalmode vibrations are of greatest magnitude.

In FIG. 1 frequency f₁, approximately 24.45 kHz, is the frequencyassociated with the first one of the mechanical resonant modes of ahandpiece. This frequency is the resonant frequency of this resonantmode when the tip is in the unloaded state. A tip is in the unloadedstate when the tip is vibrating in free space. When the tip is appliedto tissue, the load of the tip increases above the free space load. Thisresults in a change of the resonant frequency (or frequencies) of themechanical resonant mode (or modes). The resonant frequency (orfrequencies) of the tip may also change for other reasons. These reasonsinclude changes in tip temperature or changes in the acoustic propertiesof the load applied to the tip. This is why PCT Pub. No. WO 2015/021216A1 teaches one to continually evaluate whether or not Equation (1) teststrue. As a result of the tip being applied to tissue the resonantfrequency of the mechanical resonant mode changes. Thus, to ensureefficient operation of the system, including the tip, why PCT Pub. No.WO 2015/021216 A1 teaches one to, based on Equation (1), continuallyadjust the drive signal applied to the handpiece so the signal is at afrequency that as closely as possible matches the real time resonantfrequency of the relevant mechanical resonant mode.

Some tips are now available that are designed to substantially reducethe undesirable effects caused by longitudinal movement of the tip shaftadjacent the tip head. Typically this tip is designed to simultaneouslyvibrate in two modes. Often this tip is designed to vibrate in both thelongitudinal mode and the torsional mode. One tip capable ofsimultaneously vibrating in these two modes is the Long Micro Claw tipavailable from the Applicant, Stryker Corporation, of Kalamazoo,Michigan. The structure of this tip is disclosed in U.S. Pat. No.6,955,680, COUPLING VIBRATION ULTRASONIC HAND PIECE, the contents ofwhich is explicitly incorporated by reference. In brief, this type oftip has features that breakdown the longitudinal vibrations that aretransmitted from the drivers are broken down into two components.Specifically, these features breakdown the vibrations so that eachvibration has a longitudinal component, a longitudinal mode vibration,and a torsional component, a torsional mode vibration.

The tip head vibrations are vibrations that equal the sum of thelongitudinal mode vibrations and sum of the torsional mode vibrations.

The above-described tip has, in the relevant frequency range, twomechanical resonant modes. In FIG. 1 , frequency f₁ is the resonantfrequency associated with the first mechanical resonant mode. Frequencyf₂, 25.32 kHz is the resonant frequency associated with the secondmechanical resonant mode. When the tip is vibrated at the mechanicalresonant frequency associated with the first mechanical resonant mode,the distal portion of the tip undergoes a both a longitudinal movementand a torsional movement that are at peak range in comparison the rangesof movement when the drive signal is either slightly below or slightlyabove this resonant frequency. When the tip is vibrated at themechanical resonant frequency associated with the second mechanicalresonant mode, the distal portion of the tip undergoes both alongitudinal movement and a torsional movement that are at peak range incomparison to the range of movement when the drive signal is eitherslightly below or above this resonant frequency. For tips to which adrive signal of approximately 25 kHz is applied, the definition of“slightly below” may be a frequency of 100 to 300 Hz below themechanical resonant frequency. For this type of tip, the definition of“slightly above” may be a frequency of 100 to 300 Hz above themechanical resonant frequency.

Often the peak range of motion produced when the tip is vibrated at oneof the mechanical resonant modes is a larger range of movement than thepeak range of movement when the tip is vibrated at the frequencyassociated with the other mechanical resonant mode. The above-mentionedincorporated by reference PCT Pub. No. WO 2015/021216 A1 teaches oneapply source a drive signal that causes the tip to vibrate at theresonant frequency of the mechanical resonant mode at which the peakrange of motion has the largest magnitude. In FIG. 1 this is frequencyf₁.

The Applicant's PCT App. No. PCT/US2015/044023, published as WO2016/022808 A1/US Pat. Pub. No. 10,561,435 B2, the contents of which areincorporated herein by reference discloses an alternative system forregulating the application of the drive signal applied to the handpiece.This document is directed to a system that discloses how a drive signalthat has plural components can be applied to the handpiece. A firstcomponent of the drive signal has a potential and is at frequencyassociated with the first mechanical resonant mode, frequency f₁ in FIG.1 . A second component of the drive signal has a potential and is at thefrequency associated with the second mechanical resonant mode. This isfrequency f₂ in FIG. 1 . By adjusting potentials and frequencies of theindividual components of the drive signal the magnitude of sum of thelongitudinal components of the vibrations associated with the twomechanical resonant modes can be adjusted. The adjustment of thepotentials of the individual components of the drive signal also setsthe magnitude of the sum of the torsional components of the vibrationsof the two resonant states. By adjusting these individual vibrationcomponents the tip can be vibrated in such a way that the tip headengages in a path of travel that can be considered non-linear. Here, anon-linear path of travel is a path of travel such that when a singlepoint on a tip head engages in a single back and forth vibratory cycle,in a first phase of the cycle the point transits over a first set ofpoints in a space, in the second phase, the return phase, the tiptransits over a second set of points in space. This second set of pointsis different from the first set of points. In one instance the path oftravel in a single cycle is essentially elliptical.

A benefit of driving the tip in a non-linear path of travel is that in afirst phase, the tooth strikes the bone and then in the next phase ofmovement rubs against the bone. During the striking phase of tip toothmovement, the tip fractures the bone to remove the desired quantity ofbone. During the phase of movement when the tooth rubs against the bone,the tooth clears away the debris just formed as result of the toothstriking phase. The clearing away of these debris results in a likereduction of the extent to which the presence of the debris during thenext vibratory cycle adversely affects the bone cutting process.

For the reasons set forth above, it is useful to apply a drive signal toan ultrasonic handpiece that causes the tip to undergo simultaneousvibrations in two vibratory modes, longitudinal and torsional.

Nevertheless, even a tip designed driven to engage both torsional modevibrations and longitudinal mode vibrations will along the shaft of thetip undergo some longitudinal movement. For the reasons set forth above,this movement can result in unwanted cavitation adjacent the distal endof the tip head and, by extension, unwanted tissue ablation.Accordingly, there are still some situations where it would be best if adrive signal could be applied to the handpiece so that the tip is forcedinto what vibrations that are substantially torsional and that have aminimal, if any, longitudinal component.

SUMMARY OF THE INVENTION

This invention is related to a new and useful ultrasonic surgical toolsystem. The system of this invention includes a handpiece with a tip andcomplementary control system for supplying a drive signal that vibratesthe tip. Collectively the console and tip are arranged so that when thedrive signal is applied to the tip the tip engages in motion that isprimarily in the torsional mode.

The system of this invention includes a handpiece with a tip. The tip ofthis invention has features that convert a component of the longitudinalvibrations into torsional vibrations.

This invention is based on the principle that, owing to thecharacteristics of the mechanical components forming the handpiece,including the tip, the handpiece has between the resonant frequencies ofthe first and second mechanical resonant modes a longitudinal mechanicalcancellation frequency. When a drive signal is applied to the handpiecedrivers at this frequency, the mechanical components of the handpieceare excited into simultaneously inducing both first and secondmechanical resonant mode vibrations in the tip. A further principle uponwhich this invention is based is that when the mechanical components areexcited into vibrating simultaneously in the two mechanical resonantmodes, the longitudinal vibrations associated with the resonant modesare out of phase with each other and the torsional vibrations are inphase.

As a result of the handpiece being so vibrated, since the longitudinalvibrations of the individual modes are out of phase, these vibrationscancel each other out. Since the torsional vibrations of the individualmodes are in phase, the tip, more particularly, the head and theadjacent section of the shaft, engage in appreciable torsionalvibrations. Thus the tip head of this invention undergoes substantialtorsional vibrations while the head and the adjacent section of theshaft undergo minimal, if any longitudinal vibrations.

This invention is directed to a system that, by monitoring thecharacteristics of the drive signal applied to the handpiece,continually adjusts characteristics of the drive signal. Moreparticularly the frequency of the drive signal is continually adjustedto ensure that this signal, as closely as possible, equals thelongitudinal mechanical cancellation frequency of the handpiece.

This continual monitoring of the drive signal and subsequent adjustmentof the frequency of this signal is necessary because, as the loadapplied to the mechanical components of the handpiece change, thelongitudinal mechanical cancellation frequency likewise shifts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the claims. The aboveand other features and benefits of the invention are further understoodfrom the following Detailed Description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a graphical representation of the real component of the ratiobetween the current due to the capacitance of the handpiece drivers tothe mechanical equivalent of current through the handpiece overfrequency for a handpiece, including a handpiece of this invention.

FIG. 2 depicts the basic components of an ultrasonic tool system thatincludes the features of this invention;

FIG. 3 is a diagrammatic and exploded depiction of the mechanicalcomponents of the tool, the handpiece, tip and sleeve of the system;

FIG. 4 is a block diagram depicting the electrical components of thehandpiece and tip and how these components are connected to the controlconsole;

FIG. 5 depicts types of data stored in the memory internal to thehandpiece;

FIG. 6 depicts types of data stored in the memory integral with the tooltip;

FIG. 7 is a block diagram of the electrical components of the controlconsole and handpiece components of the system of this invention;

FIG. 8 represents in two dimensions, the path of travel of a point ofthe tip head around the longitudinal axis when the tip is vibratedaccording to this invention;

FIG. 9 is a diagrammatic indication of the location of the boundariesand nodes associated with longitudinal and torsional vibrations of thehandpiece, including the tip;

FIG. 10 is a diagrammatic representation of during a first phase of avibratory cycle, the individual components of the longitudinal andmechanical vibrations of the handpiece and the sum of these components.

FIG. 11 is a diagrammatic representation of during a second phase of avibratory cycle, the individual components of the longitudinal andmechanical vibrations and the sum of these vibrations;

FIG. 12 is a schematic diagram of the impedances through whichelectrical current and mechanical equivalent are applied according tothis invention; and

FIGS. 13A and 13B, when assembled together, form a flow chart of theoperation of the system of this invention.

DETAILED DESCRIPTION I. System Overview and Hardware

An ultrasonic tool system 30 that includes the features of thisinvention is now generally described by reference to FIGS. 2 and 3 .System 30 includes a handpiece 32. A tip 142 is attached to and extendsdistally forward from the handpiece 32. (“Distal” is understood to meanaway from the practitioner, towards the site to which the handpiece isapplied. “Proximal” is understood to mean towards the practitionerholding the handpiece, away from the site to which the handpiece isapplied.) Tip 142 is the component of system 30 that is applied totissue to perform the desired medical/surgical procedure. System 30 alsoincludes a control console 230. Control console 230 sources a drivesignal that is applied to the handpiece 32. In response to applicationof the drive signal, handpiece 32 causes tip 142 to vibrate.

Handpiece 32 includes a body or shell 34, seen only in FIG. 2 . FromFIGS. 3 and 4 it can be seen that one or more vibrating piezoelectricdrivers 36 (four shown) are disposed inside the shell 34. Each driver 36is formed from material that, when a current iS applied to the driver,undergoes a momentary expansion or contraction. The driverexpansions/contractions are on the longitudinal axis of a driver 36, theaxis that extends between the proximally and distally directed faces ofthe driver. A pair of leads 38 extends away from each driver 36. Leads38 are attached to the opposed proximally and distally directed faces ofthe drivers. Many, but not all, handpieces 32 include drivers 36 thatare disc shaped. Drivers 36 are arranged end to end in a stack. Leads 38are the components of system 30 over which the drive signal is appliedto the drivers 36. Optional insulating discs 40, one shown, are disposedbetween adjacent drivers 36. In FIG. 3 drivers 36 and the insulatingdisc 40 are shown spaced apart from each other. This is for ease ofillustrating the components. In practice, drivers 36 and insulatingdiscs 40 tightly abut.

A post 44 extends longitudinally through the drivers 36, leads 38 andinsulting discs. The post 44 extends through the drivers 36, leads 38,and insulating discs 40 and along the collinear longitudinal axes ofthese components. Not seen are through bores internal to the drivers 36,leads 38 and insulating discs 40 through which the post 44 extends. Post44 projects outwardly of both the most proximally located driver 36 andthe most distally located driver.

A proximal end mass 46 is located adjacent and abuts the proximallydirected face of the most proximally located driver 36. Mass 46 isattached to the proximal end section of post 44. If post 44 is threaded,mass 36 may be a nut.

A horn 48, seen in FIG. 3 , extends forward from the distally directedface of the most distally located driver 36. Horn 48 has a base with adiameter approximately equal to the diameter of the drivers 36.Extending distally forward from the drivers 36, the diameter of the horn48 decreases. The exposed distal end section of post 44 is affixed tothe horn 48. In many versions of the invention, post 44 and horn 48 area single piece unit. Handpiece 32 is constructed so that the stack ofdrivers 36 and insulating discs is compressed between proximal mass 46and horn 48.

Also disposed in handpiece shell 34 is a handpiece memory 56. Memory 56contains data used to regulate the operation of the handpiece 32 and tip142. Memory 56 may take the form of an EPROM, an EEPROM or an RFID tag.The structure of the memory is not part of the invention. For purposesof illustration handpiece memory 56 is an RFID tag. A coil 54 is shownconnected to memory 56. Coil 54 is the component associated with thehandpiece over which the control console 230 reads from and writes tothe handpiece memory 56.

FIG. 5 illustrates types of data stored in the handpiece memory 56.These data, as represented by field 62, include data identifying thehandpiece 32. These data are useful for verifying that the console 230is able to apply a drive signal to the handpiece. Data in field 62 mayalso indicate the type of information regarding the handpiece that ispresented on the console display 268. Other data in the handpiece memory56 are used to regulate the sourcing of drive signals to the drivers 36.While the use of these data are discussed below, the types of data arenow described. Field 64 contains data indicating the capacitance C₀, thecapacitance of the stack of drivers 36. Driver capacitance can bedetermined by analysis during the process of assembling the handpiece34. Often the sum of the capacitance of the drivers is between 500 to5000 pF. Data regarding the maximum current that should be applied tothe handpiece 36, current i_(S) ^(MAX), are contained in a field 66.Current i_(S) ^(MAX) is often less than 1 Amp peak and more often 0.5Amp peak or smaller. Field 68 contains data indicating maximum belowdiscussed mechanical equivalent of current, i_(M) ^(MAX), that shouldflow through the below discussed mechanical components of the handpiece.Current i_(M) ^(MAX) is typically 0.25 Amps peak or less. The maximumpotential of the drive signal, voltage V_(S) ^(MAX), are stored in field70. Voltage V_(S) ^(MAX) is often 1500 Volts AC peak.

Also stored in handpiece memory 56 are data indicating the minimum andmaximum frequencies of the drive signal that should be applied tohandpiece 32. The minimum frequency, stored in field 72, is typicallythe minimum frequency of the drive signal that can be supplied by thecontrol console. The maximum frequency of the drive signal, stored infield 74, is typically between 5 kHz and 40 kHz greater than the minimumfrequency.

Field 76 contains coefficients for controlling the control signalsoutput by controller 96. PID control loops are used to establish thefinal levels for each of these signals. Field 76 contains thecoefficients for each of these control loops. It should be understoodthat the data in fields 62, 66, 68, 70, 72, 74 and 76, like the data infield 64, are stored in the handpiece memory 56 as part of the processof assembling the handpiece.

Handpiece memory 56 also contains field 78 as a use history field.Control console 230, during use of the handpiece 32, writes data intofield 128 so as to provide a log of the operation of the handpiece.

Returning to FIG. 4 , it can be seen that also shown internal to thehandpiece 32 are two conductors 132. Conductors 132 extend from coil 54to the distal end of the handpiece. The conductors 132 are connected toa second coil, coil 134, also disposed in the handpiece 32.

Tip 142 extends forward from the handpiece horn 48. The tip 142 has agenerally cylindrical shaft 144. In some, but not all versions of theinvention, shaft 144 has plural sections each with a different crosssectional diameter. In the illustrated version of the invention, tipshaft 144 has a proximal section 146. Shaft proximal section 146 isformed with coupling features designed to facilitate the removablecoupling of the tip to handpiece 32. In one version of the invention,the handpiece coupling feature is a boss 49 that extends forward fromhorn 48. The outer surface of the boss 49 is formed with threading (notillustrated). The tip coupling feature is a closed end bore 145 thatextends inwardly from the proximal end of the shaft 144 partiallythrough the shaft proximal section 145. Bore 145 is provided withthreading (not illustrated) designed to engage the threaded bossintegral with the handpiece horn 48.

In the depicted versions of the invention, shaft 144 has a middlesection 150 that extends forward from the shaft proximal section 146.Middle section 150 has a diameter less than that of the proximal section146. The depicted shaft 144 has a distal section 160. Shaft distalsection 160 has a diameter less than that of the middle section 150. Notidentified are the tapered transition sections of the shaft 144. Onetransition section is between the proximal section 146 and the middlesection 150. A second transition section is between the middle section150 and the distal section 160. The distal section of the shaft has itsown slight taper such that as the section 160 extends distally thediameter of the shaft slightly decreases.

A head 164 is the most distal portion of tip 142. Head 164 is locatedimmediately forward of the shaft distal section 160. Head 164 issometimes formed with teeth or flutes (not illustrated). Tip head 164 isthe portion of system 30 pressed against tissue to perform a desiredprocedure. The teeth or flutes are designed so that when the head 164moves, the teeth or flute bear against tissue. As a consequence of themovement of the head, the teeth or flutes remove tissue. The geometry ofthe tip teeth or flutes is not part of the present invention.

Handpiece 32 is generally designed so that the back and forth movementof the drivers induce a like vibrating motion in the tip 142. These arelongitudinal vibrations in that the motion is back and forth along thelongitudinal axis of the tip and, more particularly, the shaft. A tip142 of this invention is further provided with features that convert theproximal to distal vibratory motion applied to the proximal end of theshaft 144 into two vibratory motions. In the depicted tip 142 thesefeatures are helical grooves 154 that extend inwardly from the outersurface of shaft middle section 150. Owing to the presence of grooves154, a fraction of the longitudinal motion applied to the shaft proximalsection 146 into motion that causes the more distal sections of the tipto, in addition to vibrating longitudinally, vibrate rotationally.Rotational vibration is understood to mean the vibration of the shaftand tip in an arc that extends around the longitudinal axis of the shaft144.

A sleeve 170 is disposed around tip shaft 144. Sleeve 170 is formed ofplastic. The proximal end the sleeve is formed with features thatfacilitate the releasable coupling of the sleeve to the distal end ofthe handpiece shell 34. The components forming system 30 are formed sothat sleeve is spaced radially away from tip shaft 144 andlongitudinally away from tip head 160. More specifically the componentsare dimensioned so that during the normal vibration of the tip, the tipdoes not abut the sleeve.

While not part of the present invention, it can be seen that sleeve 170is often formed with a fitting 172. Fitting 172 is formed to receive anirrigation line. During use of system 30, irrigating fluid is oftenflowed into the sleeve 170. The fluid flows around through the gapbetween the tip 142 and the sleeve 170 and out the open distal end ofthe sleeve. Handpiece post 44 and the tip 142 are formed with contiguousbores (bores not illustrated). During a procedure, suction is drawnthrough these bores. The suction draws from the site to which tip head164 is applied the irrigating fluid as well as debris formed by theprocedure that are entrained in the fluid. The suction also draws tissuetowards the tip head 164. This drawing of the tissue towards the tiphead 164 enhances the cutting of the tissue by the tip head.

Disposed inside the sleeve is a tip memory 184, seen as a dashedrectangle in FIG. 3 . Memory 184 is referred to as the tip memorybecause, even though the memory is disposed in sleeve 170, the memory isused to control the operation of the tip 142. Further, tip 142 andsleeve 170 are typically distributed together as a single package. Tip142 is typically initially first coupled to the handpiece 32. After thetip 142 is in place, the sleeve 170 is fitted to the handpiece. Tipmemory 184 is typically the same type of memory as handpiece memory 56.Accordingly, in the illustrated version of the invention, tip memory 184is an RFID tag. A coil 182, seen only in FIG. 4 , embedded in sleeve 170is connected to the input pins of the tip memory 172. The componentsforming system 30 are constructed so that when the sleeve 170 is fittedto the handpiece 32, handpiece coil 134 and coil 182 are able to engagein inductive signal exchange.

FIG. 6 depicts the type of data contained in tip memory 184. Asrepresented by field 188, these data include a tip identification field.The data in field 188 identifies the tip and is analogous to the dataidentifying the handpiece in handpiece memory identification field 112.In field 190 data are stored indicating the maximum total mechanicalequivalent of current, i_(M) ^(MAX), that should go through themechanical components of the handpiece when the specific tip 142. Field192 contains data indicating a minimum voltage V_(S) ^(MIN), of thedrive signal that should be applied to the handpiece drivers used tovibrate the tip. Field 193 contains data indicating a maximum voltage,V_(S) ^(MAX), of the drive signal that should be applied to thehandpiece drivers used to vibrate the tip.

Field 194 contains data defining a lowest possible frequency (MIN MRMFREQ.) for one of the mechanical resonant modes. Field 195 contains datadefining a highest possible frequency (MAX MRM FREQ.) for the mechanicalresonant mode for which filed 195 defines the lowest possible frequency.Typically fields 194 and 195 contain data defining the range offrequencies for the first mechanical resonant mode. This range offrequencies is a function of the difference between the frequencies ofthe first and second resonant modes. For example, if the differencebetween the frequencies of the two mechanical resonant modes is 2000 Hzor more, the range of frequencies contained in the data of fields 194and 195 may be 1000 Hz. More often, the range of frequencies around themechanical resonant frequency defined by data in in fields 194 and 195is 400 Hz or less. In more preferred versions of the invention, thefrequency range around the mechanical resonant frequency is 100 Hz orless.

Field 196 contains data defining a lowest possible frequency (MIN LCMFREQ.) of a below discussed longitudinal mechanical cancellationfrequency for the tip 142. Field 198 contains data defining a highestpossible frequency (MAX LCM FREQ.) for the longitudinal mechanicalcancellation frequency. The frequency range defined by the data infields 196 and 198 is also a function of the resonant frequencies of thetwo mechanical resonant modes. This frequency range is typicallycentered on the longitudinal mechanical cancelation frequency of the tipwhen the tip is in the no load state. The frequency range may partiallyoverlap the frequency range associated with the mechanical resonant modeat which the tip may be driven. The frequency range of the operation ofthe tip around the longitudinal mechanical cancelation frequency shouldnot though extend to the resonant frequency of the mechanical resonantmode at which the tip can be driven.

A PID coefficient field 204 contains control coefficients for thecontrol signals that for the tip may be more specific than the data inhandpiece memory PID coefficient field 76. Tip memory 184 also containsa tip use history field 206. During operation of system 30, the controlconsole 230 writes data to field 206 regarding use of the tip 142

Control console 230, now described with respect to FIGS. 2, 4 and 7 ,supplies the drive signal to handpiece 32 that results in the vibrationof tip 142. These components include a power supply 232. Power supply232 outputs a constant voltage signal typically between 1 and 250 VDC.In many versions of the invention, the maximum potential of the voltageoutput by power supply 232 is 200 VDC or less. The voltage produced bypower supply 232 is applied to a variable gain amplifier 234. A controlsignal, specifically a WAVEFORM_SET (W_S) signal, is applied toamplifier 234. The WAVEFORM_SET signal varies in both frequency andamplitude. The WAVEFORM_SET frequency is thus used to vary the gain andfrequency of the signal produced by the amplifier 234 so the amplifierproduces an output signal that varies in both potential and frequency.One such amplifier that can be incorporated into control console 230 isdisclosed in U.S. Prov. Pat. App. No. 62/159,672 the contents of whichare disclosed in the incorporated by reference PCT Pub. WO2016/183084/US Pat. Pub. No. 10,449,570 B2. More particularly, amplifier234 is capable of outputting a signal with a frequency of between 10 kHzand 100 kHz. Often the signal has a minimum frequency of 20 kHz and amaximum frequency of 40 kHz.

The output signal from amplifier 234 is applied to the primary winding244 of a transformer 238, also part of the control console 230. Thevoltage present across the secondary winding 248 of the transformer 238is the drive signal applied to the handpiece drivers 36. This voltage istypically a maximum of 1500 volts AC peak. The drive signal is appliedin parallel across the drivers 36.

Transformer 238 includes a tickler coil 246. The voltage present acrosstickler coil 246 is applied to a voltage measuring circuit 252. Based onthe signal across tickler coil 246, circuit 252 produces a signalrepresentative of the potential and phase of voltage V_(S), the voltageof the drive signal applied to the handpiece 32. A coil 254, alsodisposed in control console 230, is located in close proximity to one ofthe conductors that extends from the transformer secondary winding 248.The signal across coil 254 is applied to a current measuring circuit256. Circuit 256 produces a signal representative of the magnitude andphase of current iS, the current of the drive signal sourced to thehandpiece 32.

The drive signal present across transformer secondary winding 248 ispresent at two conductive contacts 250 attached to a socket integralwith the control console (socket not illustrated).

The drive signal is applied to the handpiece drivers by a cable 228 seenonly in FIG. 2 . In many constructions of system 30, handpiece 30 andcable 228 are a single unit. Cable 228 is connected to the controlconsole socket in which contacts 250 are located.

In versions of the invention wherein the handpiece 32 and cable 228 area single unit, handpiece coil 54 is disposed in the plug integral withthe cable. Disposed in the console socket is a complementary coil 258.The components forming the system are configured so that when the plugintegral with cable 228 is seated in the handpiece socket, coils 54 and258 are able to inductively exchange signals.

The signals representative of the drive signal voltage V_(S) and currenti_(S) are sourced to the handpiece are applied to a processor 266 alsointernal to the control console 230. Control console 230 also includes amemory reader 262. Memory reader 262 is connected at one end to consolecoil 258 and at an opposed end to processor 266. The memory reader 262converts the signals present across the coil 258 into data signalsprocessor 266 is able to read. Memory reader 262 also, in response tosignals output by the processor 266, output signals across coil 258 thatcause the coil to output signals that result in the writing of data tothe handpiece memory 52 and tip memory 184. The structure of memoryreader 262 complements the handpiece memory 102. Thus, memory reader 262can be: an assembly capable of reading data in an EPROM or EEPROM or anassembly capable of interrogating and reading data from an RFID tag.

Processor 266 generates the WAVEFORM_SET signal that is applied toamplifier 234. The processor 266 thus sets the characteristics of thedrive signal output by the control console 230 and applied to thehandpiece 32. The characteristics of the drive signal set by processor266 are the voltage and frequency of the drive signal. Processor 266determines these characteristics as a function of the characteristics ofthe handpiece 32 and the characteristics of the tip 134. Processor 266also determines the drive signal as a function of the acquiredmeasurements of voltage V_(S) and current i_(S).

A display 268 is built into control console 230. The image on display268 is shown as being generated by processor 266. Information depictedon display 268 includes: information identifying the handpiece 32 andthe tip; and information describing characteristics of the operatingstate of the system. Display 268 is often a touch screen display.Processor 266 causes images of buttons to be presented on the display.By depressing the buttons, the practitioner is able to set what he/shedesires as specific operating characteristics of the system 30.

In addition to the buttons presented on the display 268, there istypically at least one on on/off switch associated with the controlconsole. In FIGS. 2 and 7 , this on/off switch is represented by afootswitch 270. Footswitch 270 is configured to generate a signal thatvaries with the extent to which the switch is depressed. The signal issourced to processor 266. Based on the state of the signal sourced bythe footswitch 270, processor 266 regulates the generation of the drivesignal so as to control both whether or not the tip vibrates and themagnitude of the tip head vibrations.

II. Fundamentals of Operation

System 30 of this invention is designed so that the control console 230outputs a drive signal that results in the tip head 164 moving along apath of travel that can be considered substantially torsional. Here asubstantially torsional path of travel is understood to be a path oftravel, line PT of FIG. 8 , for a point on the tip head 164, is at anacute angle α that is 30° or less, preferably 15° or less and, morepreferably, 8° or less relative line PA. Line PA is understood to beperpendicular to line LA, the longitudinal axis through tip 142. Line LAand line PA are understood to be in the plane of FIG. 8 . In FIG. 8 ,line PT represents in two dimensions, the path of travel of the singlepoint of the tip head. Thus to the left of where lines LA, PA and PTintersect, line PT extends below line PA and out of the plane of FIG. 8. To the right of where lines LA, PA and PT intersect, line PT extendsabove line PA into the plane of FIG. 8 . Thus the path of travel aroundwhich a point on head 164 would move if the head engaged insimultaneously torsional and longitudinal movement is one in which thepoint would both rotate partially around line PA and move up and downalong a longitudinal path of travel parallel to line LA. Under perfectconditions, the tip head 164 engages in torsional motion and does notengage in any longitudinal motion. If the tip head 164 engages in thistype of motion it is understood that the acute angle between and line PAand line PT would be 0°.

A primary principle upon which operation of system 30 is based is that,owing to the presence of grooves 154, the features that convert thelongitudinal motion of the tip into torsional motion, the handpiece,including the tip, have first and second mechanical resonant modes thathave resonant frequencies that are spaced apart from each other. Formany versions of the system to operate where the drive signals are inthe range of 20 kHz to 40 kHz the resonant frequencies of the twomechanical resonant modes should be spaced apart by at least 250 Hz. Inmore preferred versions of the invention, these resonant frequencies arespaced apart by at least 500 Hz.

A first corollary principle upon which operation of the system is basedis that when a drive signal is applied to the handpiece drivers 36 thatis at the resonant frequency associated with the first mechanicalresonant mode, the tip head undergoes a combined longitudinal andtorsional vibration at this frequency. The tip head does not engage inappreciable vibratory motion that can be associated with the secondmechanical resonant mode.

A second corollary principle upon which operation of the system is basedis that when a drive signal is applied to the handpiece drivers 36 thatis at the resonant frequency associated with the second mechanicalresonant mode, the tip head undergoes a combined longitudinal andtorsional vibration at this frequency. The tip head does not engage inappreciable vibratory motion that can be associated with the firstmechanical resonant mode.

The boundaries and nodes of the vibrations associated with the handpieceare now described with reference to FIG. 9 . The proximal end of theproximal end mass 46 represents the proximal unconstrained boundary ofthe longitudinal vibrations of the handpiece. Here the handpiece isunderstood to include the tip 142. Distally forward of the proximalunconstrained longitudinal boundary there is a first longitudinal node,the proximal longitudinal node. This node may be located adjacent thedistal most driver 36. Forward of the proximal longitudinal node thereis the second longitudinal node, the distal longitudinal node. This nodeis located in the tip 142 at a location proximal to the helical grooves154. At the longitudinal nodes, the longitudinal expansion/contractionwaves the drivers induce in the handpiece neither expand nor contractthe handpiece or tip. On the opposed sides of each longitudinal nodes,the acoustic waves generated by the drivers induce opposed expanding andcontracting movements of the handpiece. Thus, when during each resonantmode of the handpiece, the drivers induce expansion of the handpiecebetween proximal unconstrained boundary and the proximal longitudinalnode, there is contraction between to the two longitudinal nodes andexpansion distal to the distal longitudinal node. Similarly, when, for aresonant mode, the drivers induce contraction between the proximalunconstrained boundary and the proximal longitudinal node, the handpieceundergoes expansion between the longitudinal nodes and, distal to thedistal longitudinal node, contraction.

At a location distal to the distal longitudinal node and proximal togrooves 154, the handpiece has a fixed torsional boundary. Distal tothis location, owing to the presence of grooves 154, a fraction of eachlongitudinal expansion/compression wave that passes through the tip, isconverted into motion that twists the tip, induces a torsional motion.Forward of the grooves 154, there is a torsional node. At the torsionalnode the tip does not engage in any torsional motion. Distal to thetorsional node, the tip twists in a direction opposite the direction inwhich the section of the tip between the fixed torsional plane and thetorsional node twists.

The distal end of the tip head 164 is the unconstrained boundary forboth the longitudinal and torsional vibrations of the handpiece. Thisboundary is an unconstrained boundary because the tip head is notattached to a fixed object that constrains the motion of the tip. Thisis why, when a drive signal is applied to the handpiece, the vibratorymotions transmitted through the tip shaft 144 to the tip head 164 inducevibratory movement of the tip head.

When a drive signal is applied to the handpiece drivers at a frequencybetween the first and second mechanical resonant modes, the mechanicalcomponents of the handpiece are driven to simultaneously engage in theplural vibrations associated with each of the first and secondmechanical resonant modes. Thus, when a drive signal is applied to thehandpiece drivers at a frequency between the resonant frequencies of thefirst and second mechanical resonant modes, the force the drivers 36apply to the rest of the handpiece induces longitudinalexpansions/contractions that have a component associated with the firstmechanical resonant mode and a component associated with the secondresonant mode. It is further understood longitudinal vibrationsassociated with the second mechanical resonant mode are out of phasewith the longitudinal vibrations associated with the first mechanicalresonant mode.

Similarly, when a drive signal is applied to the handpiece drivers atthe frequency between the resonant frequencies of the first and secondmechanical modes, the mechanical components of the tip 142 distal togrooves 154 engage in torsional vibrations that have a componentassociated with the first mechanical resonant mode and a componentassociated with the second mechanical resonant mode. It is furtherunderstood that the torsional vibrations of the tip associated with thesecond resonant mode are in phase with the torsional vibrations of thetip associated with the first resonant mode. This means when the tipengages in a longitudinally contracting (or expanding) motion due tobeing vibrated in the second mechanical resonant mode, the tip is forcedinto torsional motion in the same direction as when the tip is engagesin a longitudinal expanding (or contracting) motion due to beingvibrated in the first mechanical resonant mode.

Based on the these principles, system 30 of this invention is configuredto apply a drive signal to the handpiece drivers 36 that is between theresonant frequencies associated with the first and second mechanicalresonant modes of the handpiece. The particular frequency at which thedrive signal is applied to the drivers is what is now referred to as thelongitudinal mechanical cancellation frequency, f_(LC). In the plot ofFIG. 1 , the longitudinal mode cancellation frequency f_(LC) is 24.97kHz.

When a drive signal is applied to the drivers 36 at the longitudinalmechanical cancellation frequency, the handpiece operates in what isreferred to as the longitudinal mechanical cancellation mode. FIGS. 10and 11 illustrate the components of the vibratory movements of the tipwhen the handpiece operates in this mode. FIG. 10 depicts what happenswhen the drivers apply a first force to the rest of the handpiece.Arbitrarily the drivers are outputting an expanding force represented byoutwardly directed double head arrow 280. The drivers can be consideredto apply this force to the other mechanical components of the tip duringthe first phase of a single vibratory cycle. For the purposes of thisinvention, the mechanical components of the handpiece are the vibratingcomponents of the handpiece that apply mechanical energy to a mechanicalload. These components include drivers 36, post 44, proximal end mass 46horn 48 and tip 142. Sleeve 170 is typically not considered a componentto which the equivalent of current flows. This is because, while thesleeve 170 vibrates, the vibration of the sleeve is due to the vibrationof the other components. In other words, the sleeve 170 is part of themechanical load to which the vibrations of the other mechanicalcomponents of the handpiece are applied. Accordingly, sleeve 170, forthe purposes of analyzing the motion and signal flow of this invention,is not considered one of the mechanical components of the handpiece.

As a result of the drivers 36 applying an expanding force to the rest ofthe handpiece at the longitudinal mechanical frequency, the mechanicalcomponents of the handpiece are excited into undergoing their ownlongitudinal movement. Owing to the tendency of these components tovibrate at the first mechanical resonant mode, distal to the distallongitudinal node, this movement is a longitudinally expanding movement.This is represented by right directed arrows 284 of FIG. 10 . While thismovement is like the movement of the drivers is an expanding movement,this movement is out of phase with the vibrations of the drivers 36.Owing to the presence of the helical grooves 154, at the torsionalboundary, a fraction of this longitudinal movement is converted intotorsional movement of the tip 142. Adjacent the torsional boundary thismovement is in the direction of curved arrow 288. Looking down thehandpiece from the distal end, this movement would appear as acounterclockwise motion. At locations along the tip from the torsionalnode to the tip head, this movement would, from the same perspectiveappear as a clockwise rotation, the rotation represented by arrow 290.

The mechanical components of the handpiece also want to vibrate at thesecond mechanical resonant mode. Accordingly, the application of thesame expanding force applied to mechanical components of the handpiecethat causes out of phase longitudinal expanding vibrations of thesecomponents in the first mode, induces these same components, distal tothe distal longitudinal node, into out of phase longitudinallycontracting vibrations in the second mechanical resonant mode. Thesecontracting vibrations are represented by left directed arrows 292.Owing to the presence of helical grooves 154 distal to the torsionalboundary a fraction of these longitudinal vibrations are converted intotorsional vibrations. Immediately adjacent the torsional boundary, thesevibrations as represented by curved arrow 294, are in thecounterclockwise direction. Distal to the torsional node, thesevibrations, as represented by arrow 296 are in the clockwise direction.

Thus, when a drive signal at the longitudinal mechanical cancellationfrequency is applied to the drivers 36, during one phase of the signal,the tendency of the handpiece mechanical components to expand distal tothe longitudinal node is cancelled out by the tendency of thesecomponents to also want to contract. The tip head 164 thereforeessentially does not engage in longitudinal movement.

Simultaneously in this phase, the opposed forces that would otherwiseinduce the longitudinal motion of the handpiece components are, asresult of the presence of helical grooves 154, converted into torsionalmotion distal to the torsional boundary. These torsional motions are inphase with each other as represented by arrows. Since these torsionalmotions are in phase with each other, they are cumulative. In otherwords, during a phase of a vibration cycle the torsional movement of thetip head 164 is greater than the torsional movement of the tip head ifthe tip head was excited into a torsional movement owing the handpiecebeing driven to vibrate at a single one of the mechanical resonantfrequencies. This is why, in FIG. 10 , the curved arrow 302 thatrepresents the sum of the torsional vibrations proximal to the torsionalnode is depicted as being longer than either one of arrows 288 and 294.For the same reason, curved arrow 304 that represents the sum of thetorsional vibrations distal to the torsional node is depicted as longerthan either one of arrows 290 and 296.

FIG. 11 depicts what happens when the drivers 36, during the secondphase of a single vibratory cycle, apply a contracting force. As aresult of the drivers contracting, post 44 pulls nut 46 and horn 48towards each other is represented by inwardly directed double head arrow310. As a result of the application of this force, and the tendency ofthese components to want to vibrate at the first mechanical resonantmode, distal to the distal longitudinal node this force appears as alongitudinally contracting movement. This movement is represented by theleft directed arrows 312 of FIG. 11 . This movement is out of phase withthe contractions of the drivers 36. Owing to the presence of the helicalgrooves 154, at the torsional boundary, a fraction of this longitudinalmovement is converted into torsional movement of the tip 142. Adjacentthe torsional boundary this movement is in the clockwise direction ofcurved arrow 314. At locations along the tip from the torsional node tothe tip head 164, this movement would, from the same perspective, appearas a counterclockwise rotation, the rotation represented by arrow 316.

The mechanical components of the handpiece also want to vibrate at thesecond mechanical resonant mode. Accordingly, the application of thesame contracting force applied to mechanical components of the handpiecethat causes out of phase longitudinal contracting vibrations of thesecomponents in the first mode, induces these same components, distal tothe distal longitudinal node, into out of phase longitudinally expandingvibrations in the second mechanical resonant mode. These expandingvibrations are represented by right directed arrows 320. Owing to thepresence of helical grooves 154 distal to the torsional boundary afraction of these longitudinal vibrations are converted into torsionalvibrations. Immediately adjacent the torsional boundary, thesevibrations as represented by curved arrow 322, are in the clockwisedirection. Distal to the torsional node, these vibrations, asrepresented by arrows 324 are in the counterclockwise direction.

So the sum of the vibratory movement of the handpiece in this secondphase of a vibration cycle is the partial inverse of the vibratorymovement in the first phase of the cycle. Again, the longitudinalvibrations, which are out of phase with each other, cancel each otherout. This is why there is substantially minimal longitudinal movement ofthe tip. The torsional vibrations associated with the two mechanicalresonant modes are in phase. This is why the tip 142 engages a torsionalmovement, a twist. As represented by the relative lengths of curvedarrows 326 and 328 to curved arrows 314, 316, 322 and 324, this twist isgreater in magnitude than the twist induced due to the tendency of thehandpiece to want to vibrate either a single one of the mechanicalresonant modes.

Consequently, when a drive signal at the longitudinal mechanicalcancellation frequency is applied to the drivers 36, the handpiecemechanical components are driven to vibrate in a pattern, in which thereis substantial torsional, twisting, vibration of the head with onlyminimal, if any, longitudinal movement of the shaft 144 and tip head164.

An understanding of the characteristics of the drive signal applied tothe drivers 36 so as to cause the handpiece to vibrate at thelongitudinal mechanical cancellation frequency is obtained by initialreference to FIG. 12 . This Figure represents the current flows throughthe components of the handpiece. The current of the drive signal, i_(S),can be considered to be applied in parallel through three sets ofcomponents. The first set of components consists of the drivers 36themselves. The impedance through these components, Z₀, is essentiallythe reactance of the drivers:

$\begin{matrix}{Z_{0} = \frac{1}{j\omega C_{0}}} & (2)\end{matrix}$

Driver capacitance is, for the purposes of this invention, constant.Therefore, the only variable that affects driver impedance is ω, thefrequency in radians of the drive signal.

The second set of components through which the drive signal current iSi_(S) applied are the mechanical components of the handpiece that causethe handpiece to vibrate at the first mechanical resonant mode. Thiscurrent, it is understood, is not an actual electrical current. Instead,this current iS a mechanical equivalent of current that flows throughthese components to induce the mechanical vibrations of thesecomponents. These components include drivers 36, post 44, proximal endmass 46 horn 48 and tip 142. Again, sleeve 170 is part of the mechanicalload to which the vibrations of the other mechanical components of thehandpiece are applied. Accordingly, it should be understood that sleeve170 is not one of the components through which the mechanical equivalentof current flows.

In FIG. 12 this mechanical equivalent of current iS i₁ since it isassociated with the first mechanical resonant mode vibrations of thehandpiece is more specifically the first resonant mode mechanicalequivalent of current for the handpiece. The impedance Z₁ through whichthis mechanical equivalent is applied has: a resistive component due tothe resistive characteristics, R₁, of the handpiece mechanicalcomponents when vibrating in the first mechanical resonant mode; aninductive reactance component due to the inductive characteristics, L₁,of the handpiece mechanical components when vibrating in the firstmechanical resonant mode; and a capacitive reactance component, C₁, dueto the capacitive characteristics of the handpiece mechanical componentswhen vibrating in the first mechanical resonant mode. This impedance,Z₁, is therefore calculated based on the following equation:

Z ₁ =R ₁ +jωL ₁+1/jωC ₁  (3)

As the load to which this handpiece mechanical components changes, theresistive, inductive and capacitive characteristics of these componentschange. This is why in FIG. 12 , R₁, L₁, and C₁ are shown as variables.

The second set of components through which a portion of the drivecurrent i_(S) is applied are the mechanical components of the handpiecethat cause the handpiece to vibrate at the second mechanical resonantmode. This portion of the current, current i₂, can be considered thesecond resonant mode mechanical equivalent of current through thehandpiece. The impedance Z₂ through which the mechanical equivalent ofcurrent i₂ is applied has: a resistive component due to the resistivecharacteristics, R₂, of the handpiece mechanical components whenvibrating in the second mechanical resonant mode; an inductive reactancecomponent due to the inductive characteristics, L₂, of the handpiecemechanical components when vibrating in the second mechanical resonantmode; and a capacitive reactance component, C₂, due to the capacitivecharacteristics of the handpiece mechanical components when vibrating inthe second mechanical resonant mode. This impedance is thereforecalculated based on the following equation:

Z ₂ =R ₂ +jωL ₂+1/jωC ₂  (4)

As mentioned above, changes in the load to which the mechanicalcomponents of the handpiece are applied result in changes in theresistive, inductive and capacitive characteristics of the handpiece.Accordingly, in FIGS. 12 , R₂, L₂, and C₂ are shown as variables.

Mathematically, and given Kirchhoff's Current Law, the above breakdownof the drive signal current i_(S) can therefore be broken down asfollows:

i _(S) =i ₀ +i ₁ +i ₂  (5A)

Rearranging Equation (5A) results in the following relationship:

i ₁ +i ₂ =i _(S) −i ₀  (5B)

This means that the mechanical equivalent of current through themechanical components of the handpiece is equal to the differencebetween the current of the drive signal and the current flow throughdrivers 36. Given Equation (2),

i ₀ =jV _(S)2πfC ₀  (6)

Here f is the angular frequency of the drive signal.Substituting Equation (6) into Equation (5B) yields the followingresult:

i ₁ +i ₂ =i _(S) −jV _(S)2πfC ₀  (7)

The longitudinal mechanical cancellation frequency is above the resonantfrequency of the first mechanical resonant mode. Therefore, when a drivesignal at the longitudinal mechanical cancellation frequency is appliedto the handpiece, impedance Z₁ is primarily inductive, due jωL₁. Thelongitudinal mechanical cancellation frequency is below the resonantfrequency of the second mechanical resonant mode. Therefore, when adrive signal at the longitudinal mechanical cancellation frequency isapplied to the handpiece, impedance Z₂ is primarily capacitive due to1/jφC₂. This means that when a drive signal at the longitudinalmechanical cancellation frequency is applied to the drivers 36,impedance Z₁ is 180° out of phase with impedance Z₂. The reactivecomponents of Z₁ and Z₂ therefore essentially cancel each other out.This means that when the drive signal at the longitudinal mechanicalcancellation frequency is applied to the handpiece the parallelimpedance of Z₁ and Z₂ is purely resistive.

At the longitudinal mechanical cancelation frequency, as at anyfrequency, impedance Z₀ of the drivers 36 is purely capacitive.

The above impedances being present when a drive signal at thelongitudinal mechanical cancellation frequency is applied to the driversmeans that when the handpiece is in this state that phase angle betweencurrent i₀ and mechanical equivalent of current i₁+i₂ is 90° out ofphase.

Since both the electrical current and mechanical equivalent of currentsthrough the handpiece have a magnitude and phase, these currents can berepresented in polar form:

i ₀ =Ae ^(jθi) ⁰   (8)

and

i ₁ +i ₂ =Be ^(jθi) ^(i) ^(+ii) ²   (9)

Dividing i₀ by i₁+i₂ when they are 90° out of phase therefore leads tothe following:

$\begin{matrix}{\frac{i_{0}}{i_{1} + i_{2}} = {\frac{Ae^{j\Theta_{i_{0}}}}{Be^{j\Theta_{i_{i} + {ii}_{2}}}} = {\frac{Ae^{j\Theta_{i_{0}}}}{Be^{j({{\Theta i_{0}} - {\pi/2}})}} = {\frac{A}{B}e^{j{\pi/2}}}}}} & \left( {10A} \right)\end{matrix}$

Converting the right side of Equation (8A) to a rectangular number leadsto the following:

$\begin{matrix}\frac{i_{0}}{i_{1} + i_{2}} & = & {{\frac{A}{B}{\cos\left( {\pi/2} \right)}} + {j\frac{A}{B}{\sin\left( {\pi/2} \right)}}} & \left( {10B} \right) \\ & = & {j\frac{A}{B}} & \left( {10C} \right)\end{matrix}$

The end result of Equation (10C) is based on the fact that, the cosineof 90° is zero and sine of 90° is one.

The above result means that, when the drive signal is at thelongitudinal mechanical cancellation frequency, the real component ofthe ratio of electrical current flow through the drivers 36 and themechanical equivalent of current through the mechanical components ofthe handpiece equals zero. Mathematically:

$\begin{matrix}{{{Re}\left\{ \frac{i_{0}}{i_{1} + i_{2}} \right\}} = 0} & \left( {11A} \right)\end{matrix}$

Substituting Equations (5) and (7) into Equation (11A) means that whenthe drive signal is at the longitudinal mechanical cancellationfrequency,

$\begin{matrix}{{{Re}\left\{ \frac{jV_{s}2\pi fC_{0}}{i_{s} - {jV_{s}2\pi fC_{0}}} \right\}} = 0} & \left( {11B} \right)\end{matrix}$

The antecedent and consequent of Equation (11B) are identical to theantecedent and consequent of the prior art Equation (1). There aredifferences between applying a drive signal to the handpiece so as tocause the tip head 164 to undergo a simultaneous longitudinal vibrationsand vibrations that are substantially torsional. When one wants to drivea handpiece to induce simultaneous torsional and longitudinal vibrationsin the tip head 164, the target frequency is the resonant frequencyassociated with one of the mechanical resonant modes of the tip. Oftenthis is the resonant frequency associated with the first mechanicalresonant mode. In contrast, when applying a drive signal to thehandpiece according to this invention the target frequency is thelongitudinal mechanical cancellation frequency for the tip 142. Thisfrequency is within the range of frequencies defined by the data infields 196 and 198 of the tip memory.

A second difference between two systems is that the polarity of theratio of the system of this invention is opposite the polarity of theratio of Equation (1). The reason for this is that when regulating thedrive signal so the handpiece is in a mechanical resonant mode, theslope of the relationship between the current applied to the driversover the mechanical equivalent of current applied to the handpiece tofrequency is positive. This means that by making the ratio of Equation(1) negative, should an evaluation of system state yield a negativeresult, the controller interprets the system as being in a state, inwhich in order to apply a drive signal to the handpiece that is at theresonant frequency of the resonant mode, it is necessary to increase thefrequency of the drive signal. Conversely, should the evaluation ofEquation (1) yield a positive number, the controller interprets thesystem as being in a state, in which in order to apply a drive signal tothe handpiece that is at the resonant frequency of the resonant mode, itis necessary to decrease the frequency of the drive signal.

In contrast, when regulating a system according to this invention, toapply a drive signal at the longitudinal mechanical cancellationfrequency to the handpiece, the slope of the relationship between thecurrent applied to the drivers over the mechanical equivalent of currentapplied to the handpiece to frequency is negative. As discussed abovethe ratio of Equation (11B) is of opposite polarity to the ratio ofEquation (1). This means that should an evaluation of system state ofthis invention yield a positive result, processor 266 interprets thesystem 30 as being in a state, in which, to apply a drive signal at thelongitudinal mechanical cancellation frequency to the handpiece that isat the resonant frequency of the resonant mode, it is necessary toincrease the frequency of the drive signal. Conversely, should theevaluation of Equation (11B) yield a negative number, processor 266interprets the system as being in a state, in which in order to apply adrive signal to the handpiece that is at the longitudinal mechanicalcancellation frequency, it is necessary to decrease the frequency of thedrive signal.

From the above it should also be appreciated that the total mechanicalequivalent of current through the mechanical components of the handpieceis equal to the sum of the mechanical equivalents of current through thehandpiece. Mathematically,

i _(M) =i ₁ +i ₂  (12)

III. Actual Operation

Operation of system 30 of this invention starts with the coupling of thetip 142 to the handpiece 32. Sleeve 170 is fitted over the tip and alsoattached to the handpiece. 32. Cable 228 is attached to the controlconsole 230. Console 230 is then ready to be turned on. The abovesub-steps form the initial assembly and activation of the system, step332 in FIG. 13A. When the control console 230 is initially turned on,processor 266 reads the data stored in handpiece memory 56 and tipmemory 184, step 334. The processor 266 receives these data by assertingthe appropriate commands to the memory reader 262.

Based on the read data, in a step 336, processor completes the initialconfiguration of the system. Step 336 includes the performance of anumber of evaluations to determine whether or not the system 30 isproperly configured for use. These evaluations include: determining ifthe handpiece is one to which the control console 230 can supply a drivesignal; and determining if tip 142 is one that is appropriate foractuation by the handpiece. These evaluations may be based on data fromthe handpiece identification field 62 and from the tip identificationfield 188. Processor 266 also evaluates whether or not the handpiece 32and tip 142 are in conditions for use based on the read data from thehandpiece use history field 78 and the tip use history field 218. Anexample of data indicating that use may be inappropriate are dataindicating that a particular component, the handpiece or tip, has beenused for a number of times or an overall time that exceeds the designedlife cycle for the component.

Based on the data in the handpiece memory 56, the tip memory 184 and thepractitioner commands, the processor in a step 338 established aselected maximum equivalent of current i_(M) ^(SELECTMAX) that is beflowed through the mechanical components of the handpiece. Current i_(M)^(SELECTMAX) is understood to be no greater than the maximum mechanicalequivalent of current i_(M) ^(MAX) as read from the tip memory 184.

Step 340 represents processor 266 waiting to determine if the controlmember has been actuated to indicate that the tip 142 is to be vibrated.In the described embodiment of the invention, processor 266 executesstep 340 by monitoring the signal output by footswitch 270. When thepractitioner wants to actuate the tip 142, he/she depresses thefootswitch 270. The magnitude of tip head vibrations is set by thepractitioner controlling the extent to which the footswitch 270 isdepressed.

In response to the practitioner depressing the control member, theprocessor in a step 342 calculates a target current i_(M) ^(TARGET),sometimes referred to as the target mechanical equivalent of current.Target current i_(M) ^(TARGET) is the mechanical current that theprocessor determines should be applied to the mechanical components ofthe handpiece 32. Target current i_(M) ^(TARGET) is based on currenti_(M) ^(MAX) retrieved from the handpiece memory and the extent to whichthat footswitch 270 is depressed. The target current can be calculatedusing a first order equation:

i _(M) ^(TARGET) =Di _(M) ^(SELECTMAX)  (13)

Coefficient D is between 0.0 and 1.0, inclusive. If, for example, thepractitioner depresses the footswitch 270 to have the handpiece tip 164undergo the vibrations of maximum amplitude, processor 266 setscoefficient D to unity. If the setting of footswitch 270 indicates thatthe vibrations are to be at an amplitude less than the maximum,processor 266 sets coefficient D to a value less than one.

In step 344, processor 266 then generates the initial WAVEFORM_SETsignal. The potential of this signal is set to cause the power supply tooutput a drive signal that is appreciably less than the maximum drivesignal voltage V_(S) ^(MAX) retrieved from the handpiece memory 58. Forexample, in some versions of the invention the potential of theWAVEFORM_SET signal is set cause the outputting a drive signal with apotential is between 0.02 and 0.10 of voltage V_(S) ^(MAX). Moreparticularly, the WAVEFORM_SET signal is set to cause the voltage of thedrive signal to a potential that is between 0.03 and 0.07 of voltageV_(S) ^(MAX). The relationship between the voltage of the WAVEFORM_SETsignal and drive signal voltage V_(S) of the drive signal is typically afirst order relationship. The determination of the voltage of theWAVEFORM_SET signal as a function of the target drive signal voltage isbased on potential of the target drive signal voltage and a coefficientand offset values previously stored in the processor 96.

As part of step 344, processor 266 also establishes the frequency of theWAVEFORM_SET signal. When the control member is initially depressed toactuation the handpiece, processor 266 sets the frequency of theWAVEFORM_SET signal to be between the minimum possible longitudinalmechanical cancellation frequency, the frequency from field 196 in thetip memory 184, and the maximum possible mechanical cancellationfrequency, the frequency from filed 198 in the tip memory. While notspecifically called out, in step 342 processor 344 asserts any necessaryenable signals to the power supply 232, amplifier 234 and any safetycomponents internal to the console 230. The assertion of these signalsensures that the power supply 232 outputs the necessary rail signal tothe amplifier, the amplifier 234 applies the intended signals across thetransformer primary winding 244. The drive signal is induced to developacross the secondary winding 248.

As a result of the signal flow across transformer 238, the drive signalis applied to handpiece 32. This results in the cyclicexpansion/contractions of the drivers 36. Since the drivers vibrate afrequency between the first and second mechanical resonant modes of thehandpiece, the handpiece itself engages in the simultaneous out of phasevibrations at both these resonant modes. This results in the portion ofthe tip distal to the torsional boundary engages in a vibrations thatare substantially torsional and only if nominally if at alllongitudinal.

System 30 then engages in a feedback control process to ensure that theoutput drive signal induces vibrations of appropriate amplitude anddirection in tip head 164. To perform this control, in step 346, console230 monitors the voltage V_(S) of the drive signal across the handpiece.Specifically, in step 346 the signal representative of the drive signalvoltage V_(S) output by the voltage measuring circuit 252 is applied toprocessor 266. Also in step 346, the console 230 monitors current i_(S),the current of the drive signal sourced to the handpiece 32. Thisportion of step 346 is the application of the output signal produced bycurrent measuring circuit 256 to the processor 266

In a step 348, processor 96 determines the total mechanical equivalentof current i_(M) applied to the This calculation is based on acombination of Equations (7) and (12). Processor 266 is able to makethis determination since it has data defining the four variables uponwhich this determination is based: current i_(S) from the currentmeasuring circuit 256; frequency ω based on the fact that processor setsthe frequency of the drive signal; voltage V_(S) from the voltagemeasuring circuit 252; and driver capacitance C₀. While drivercapacitance C₀ is a variable, in Equation (7) it is fixed and knownvariable read from the handpiece memory 56.

In a step 350 the total mechanical equivalent of current i_(M) iscompared to current i_(M) ^(TARGET). More particularly, this comparisonis made to determine if the actual current flow through the mechanicalcomponents of the handpiece is equal to or substantially the same as thetarget flow. Here, substantially the same is considered to be the statewhen the currents are within 20 or less mAmps of each other and moreoften 10 or less mAmps from each other, preferably 2 mAmps or less and,more preferably, 1 mAmp or smaller. Alternatively, the currents can beconsidered substantially the same if they are within 10% or less of eachother, more preferably within 5% or less of each and ideally, within 1%or less of each other.

If the currents are substantially equal, system 30 is in the state inwhich the equivalent of current applied to the mechanical components ofthe handpiece is at level at which the application of the drive signal,assumed to be at the correct frequency, is inducing vibrations ofappropriate amplitude in tip head 52. If system 30 is in this state,processor 96 proceeds to step 164.

In many situations, the comparison of step 350 indicates that the totalmechanical equivalent of current i_(M) is not substantially equal totarget current i_(M) ^(TARGET). When system 30 is in this state,processor 96 in a step 352 resets the voltage of the WAVEFORM_SETsignal. More specifically, the processor 96 calculates a value for drivesignal voltage V_(S) that would, based on Equation (7), result in anadjusted current flow through the mechanical components of the handpiecethat substantially equal to target current i_(M) ^(TARGET). Thiscalculation of step 352 is executed based on driver capacitance anddrive signal frequency remaining constant.

Not identified is the step of where, as a result of the resetting of thevoltage of the WAVEFORM_SET signal, amplifier resets the potential ofthe signal applied across the transformer primary winding 244. Thisresults in a change in the drive signal voltage V_(S) that appearsacross the transformer secondary winding 248.

In a step 356 the processor determines if the frequency of the drivesignal is at or substantially equal to the longitudinal mechanicalcancellation frequency of the handpiece. This determination is made byevaluating whether or not the ratio of Equation (11B) is equal to orsubstantially equal to zero. Here, substantially equal to zero means thereal components of the ratio is 0.10 or less, preferably 0.05 or lessand more ideally 0.01 or less.

The comparison of step 356 may indicate that the drive signal applied tothe handpiece is at or substantially equal to the longitudinalmechanical cancellation frequency of the handpiece. This is the targetstate for the drive signal. This means that the drive signal is inducingexpansions/contractions of the drivers 36 that result in the sections ofthe tip distal to the torsional boundary engaging in substantialtorsional vibrations and minimal, if any, longitudinal vibrations.

It may be determined in the evaluation of step 356 that the drive signalis not being applied to the handpiece at or near the longitudinalmechanical cancellation frequency. If processor 266 makes thisdetermination, in a step 358 the processor resets the frequency of theWAVEFORM_SET signal, step 358. If the result of the evaluation of step356 is negative, the processor 266 considers the system to be in a statein which owing to the ratio on the left side of Equation (11B) beingnegative, in step 358 processor 266 interprets the system 30 as being instate in which the frequency of the drive signal should be decreased. Ifthe calculation of step 356 yields a positive result, processor 96considers the system 30 is in a state in which it is necessary toincrease the frequency of the drive signal to ensure that the drivesignal frequency is closer to the longitudinal mechanical cancellationfrequency of the handpiece.

In step 358, processor assumes the current i_(S), voltage V_(S) anddriver capacitance C₀ are constant. In the iterative process, differentfrequencies are injected into Equation (11B). As a result of the newexecution of Equation (11B) it may be determined that the realcomponents of the ratio of the current flow through the drives and theequivalent of current applied to the mechanical components of thehandpiece is less (or substantially less) than zero. If this conditionexists, then, in the next iteration the injected frequency will be lessthan the previously injected frequency. As a result of the execution andevaluation of Equation (11B) it may be determined that the ratio isgreater (or substantially greater) than zero. If this condition exists,then, in the next iteration the injected frequency will be greater thanthe previously injected frequency. If the end result of the calculationis that the ratio is zero or substantially zero, then the frequency ofthe drive signal is set to the injected frequency. Processor 266 thenadjusts the frequency of the WAVEFORM_SET signal output to amplifier 234based on the results of these calculations. Control console 230 then, inturn, outputs a drive signal to the handpiece that is at thelongitudinal mechanical cancellation frequency of the handpiece 32.

While not shown, it is understood that characteristics of the drivesignal applied to the handpiece 32 are limited by the boundaryparameters read from the handpiece. Specifically, the adjusting of theWAVEFORM_SET signal is limited to ensure that the drive signal does notexceed the potential specified by the maximum voltage level V_(S)^(MAX). Adjustment of the WAVFORM_SET signal is further limited toensure the current of drive signal applied to the handpiece does notexceed i_(S) ^(MAX) and that the mechanical component of current doesnot exceed i_(M) ^(MAX).

It should also be understood that the adjustment of voltage andfrequency of the WAFEFORM_SET signal that occurs in steps 352 and 358are based on the PID coefficients read from the handpiece memory 56 andtip memory 184. Typically, the coefficients in the tip memory 184 arecoefficients upon which these characteristics of the WAVEFORM_SET signalare adjusted.

In FIGS. 13A and 13B, after the execution of step 356 or, if necessary,step 358, the system is shown looping back to step 340. This is becausethe processes of recalculating target current i_(M) ^(TARGET) andselectively adjusting the potential and frequency of the drive signalare generally performed as long as the system remains actuated.

There are a number of reasons why the control loop is repetitivelyexecuted. Generally, it should be understood that, if as a result of theadjustment of the frequency of the drive signal is adjusted, there willbe a change in the impedance of both driver impedance Z₀ and impedanceZ₁ and Z₂ of the mechanical components of the handpiece. This results ina change of the current flow through the handpiece and, moreparticularly, the total mechanical equivalent of current i_(M) throughthe mechanical components of the handpiece. System 30 detects thesechanges as changes in the measured values V_(S) and i_(S). Thus afterstep 356 or 358 is executed, the next evaluation of step 350 will mostlikely indicate that the system is in a state in which the totalmechanical equivalent of current i_(M) has shifted from the targetcurrent i_(M) ^(TARGET). This will necessitate a new execution of step352 to adjust the magnitude of the voltage of the drive signal.

Similarly, the adjustment of the potential of the drive signal will alsoresult in changes of voltage V_(S) and current i_(S). This means thatthe next time step 164 is executed the evaluation will indicate that thedrive signal is no longer at the longitudinal mode cancelation frequencyof the mechanical components of the handpiece.

After plural cyclings through the control loop, the console 266 assertsa drive signal that results in the current flow through the mechanicalcomponents of the handpiece that is substantially equal to i_(M)^(TARGET) and is at the longitudinal mode cancelation frequency of thehandpiece mechanical components. At start up, assuming the tip head isnot applied against tissue, it is believed that the system reaches thisstate in 2 seconds or less and, more often 1 second or less.

A further reason the control loop is continuously executed has to dowith the very nature of how handpiece 32 is employed. For the handpieceto function, the head 164 is placed against tissue, (step not shown).This is because it is the back and forth movement of the teeth againstthe tissue that result in the sawing, ablation, emulsification,collectively the removal of, the tissue. Again, in some implementationsof the invention, this back and forth movement is what results in thecavitation of the fluid adjacent the tissue and, in some instances thetissue itself.

When the head 164 is placed against tissue, a mechanical load is placedon the components forming the handpiece. This mechanical load changesthe impedance of the mechanical components of the handpiece. Here, theimpedance is understood to be the impedances associated with both thefirst and second mechanical resonant modes of the handpiece. Also, whensystem 30 is actuated, the temperature of the mechanical components ofthe handpiece often change. This change in component temperature resultsin a change in the impedances of these components. The change incomponent properties can cause a shift in longitudinal mechanicalcancellation frequency of the handpiece.

The resultant change in impedance and longitudinal mechanical cancelfrequency results in changes in the flow of both current i_(S) throughthe handpiece and the total mechanical equivalent of current i_(M). Thecontinual execution of the control loop thus ensures that when thesechanges in impedance occur, the drive signal is reset to ensure that themechanical equivalents of current i_(S) substantially equal to thetarget current i_(M) ^(TARGET) and the frequency of the drive signal issubstantially equal to longitudinal mechanical cancelation frequency ofthe mechanical components of the handpiece. The maintaining of thecharacteristics of the drive signal close to these target parametersensures that as the mechanical load to which the tip head 52 is exposedchanges, the amplitude of the vibrations of the head remainsubstantially constant and the tip head 164 and adjacent distal section160 of the shaft 144 do not engage is substantial longitudinal movement.

Further, during the time period in which the handpiece 32 is actuated,the practitioner may want to adjust the amplitude of tip headvibrations. This adjustment occurs by the resetting of control member270. (Adjustment not illustrated.) Once this adjustment occurs, in thesubsequent executions of step 148 the newly calculated target currenti_(M) ^(TARGET) will be different than the previously calculated targetcurrent. This in turn will most likely mean that as a result of the nextexecution of step 350 it will be determined that the mechanicalequivalents of current, i₁+i₂, is no longer substantially equal to thetarget current i_(M) ^(TARGET). For the reasons set forth above, thiswill most likely result in an adjusting of the potential and frequencyof the drive signal.

Accordingly, the above described control loop starting with theevaluation of step 340 is continuously executed as long the foot pedal270 or other on/off control remains actuated. The practitionerdeactivates the handpiece by releasing the foot pedal 270. This resultsin the processor, in one of the subsequent executions of step 340,receiving a signal that this control member is in the off position. Inresponse to processor 266 receiving this signal, the processor negatesthe application of the signals that were being asserted so as to causethe outputting of the drive signal, (step not shown). System 30 returnsto the wait state, the continuous monitoring of the signal from theon/off control member to determine if the practitioner wants to actuatethe handpiece 32.

It should be appreciated that after the handpiece is actuated there willeventually become a time in which it is no longer necessary to apply thevibrating tip head 164 to the tissue. The practitioner stops depressingthe control member, footswitch 270. The processor 266 detects theoccurrence of this event in the following execution of step 340. Whenthis event occurs, the processor negates the application of theWAVEFORM_SRT signal, step not shown. This results in the control consoleceasing to apply the drive signal to the handpiece drivers 36. Thisresults in the termination of the vibration of the tip 142. Processor266 continues to repeatedly execute step 340 to determine if, thepractitioner again wanting to vibrate the tip, the control member 270 isagain actuated.

System 30 of this invention is constructed so that, owing to therepetitive execution of steps 356 and 358, the system maintains thedrive signal at a frequency that is substantially equal to thelongitudinal mechanical cancellation frequency of the handpiece 32. Thisrelationship is maintained when the resonant frequency of the handpiecemechanical components changes due to the mechanical loading and/ortemperature change of these components

System 30 invention is able to vibrate the head of the tip at thedesired amplitude even when the tip and the other components of thehandpiece are subjected to mechanical loading or undergo temperaturechanges. This reduces the need for the surgical personnel using thesystem having to continuously adjust the drive signal to ensure that thetip head continuously vibrates at the desired amplitude.

Also, during the course of a procedure the tip head may be suddenlypressed against tissue. This causes a rapid significant increase in theimpedance of the mechanical components of the handpiece. In response tothis rapid change in impedance, system 30 of this invention rapidlyadjusts the potential and frequency of the drive signal. The adjustmentof these characteristics of the drive signal serve to ensure that thetip head vibrations maintain the desired amplitude. This reduces theextent to which the sudden mechanical loading of the handpiece resultsin a like sudden reduction in the amplitude of the tip head vibrations.

By applying a drive signal at the longitudinal mechanical cancellationfrequency to the handpiece, system 30 of this invention inducesvibrations in the tip 142 that are substantially torsional. The tipshaft 144 engages in minimal, if any longitudinal vibrational movement.During the course of a procedure the shaft 144 may be pressed againsttissue adjacent the tissue against which the tip head 164 is applied inorder facilitate the placement of the tip head. Since the shaft 144engages in only minimal longitudinal movement, the likelihood that thismovement could induce cavitation that would result in the unwantedremoval of the tissue against which the shaft is pressed is likewisesubstantially, if not totally, eliminated.

It likewise should be appreciated that this system does not requireprocessor 266 to match the characteristics of the handpiece 32 and tip142 to the capacitance, resistance or inductance of a component internalto the control console 230. A single console 230 can therefore be usedto construct a system 30 of this invention with different handpieces 32and tips 142, each with their own impedance characteristics. Theconsole, based on the data read from the handpiece memory 56 and tipmemory 184 configures the system 30 for each handpiece and tip assembly.Likewise, a handpiece and a tip can be used with different controlconsoles to assembly the system 30 of this invention.

It should similarly be appreciated that in the above described versionof the invention, plural different tips 142, each tip having its ownlongitudinal mechanical cancellation frequency, can be attached to andsubsequently driven by a single handpiece 32. One benefit of thisfeature of this invention is that plural different types of tips, eachwith own physical structure and therefore longitudinal mechanicalcancellation frequency can be attached to a common handpiece. A secondbenefit of this feature is that it makes possible to, post manufacture,evaluate each tip to determine the longitudinal mechanical cancellationfrequency for that tip. This means that the data for each tip used tosupply the drive signal for that tip accounts for manufacturingvariations between individual tips. Again, both types of tips that aredifferent to either basic design or manufacturing variations, can bedriven by a single handpiece. This facilitates providing a system ofthis invention that does not require the expense of providing ahandpiece that is specifically associated for use with the associatedtip 142.

System 30 of this invention is further designed to apply a mechanicalequivalent of current to the mechanical components of the handpiece thatis substantially equal to the target current. This target current isbased on the practitioner's setting of the desired amplitude of tip headvibrations. Thus, the system of this invention provides the practitionerwith a relatively accurate means of controlling the amplitude of the tiphead vibrations.

IV. Alternative Embodiments

The above is directed to one specific version of this invention.Alternative versions of the invention may have features that aredifferent from what has been described.

For example, the components used to construct this invention may bedifferent from what has been described. In some versions of theinvention, the handpiece 32 and tip 142 may be a single piece unit.

The features integral with the tip that convert the longitudinalvibratory motion into torsional vibratory motion may not always behelical grooves. In some versions of the invention, these features maybe grooves but they may not be helical. An example of an alternativegroove structure are diagonal grooves. The difference between these twogrooves is that a helical groove has a longitudinal axis that, extendingproximal to distally along the tip, curves around the longitudinal axisof the tip. A diagonal groove has a longitudinal axis that is linear inshape.

The stated frequencies, voltages, currents, capacitances and otherquantified values, unless present in the claims are understood be onlyexamples and do not limit the scope of the invention.

The control console 230 may include other components that generate thedrive signal that varies both in potential and frequency. Depending onthe construction of these components, the console may not include atransformer across which an input signal is applied in order to producethe drive signal. Similarly, in some versions of the invention, resistorcircuits as opposed to inductors may be incorporated into the console inorder to provide signal representative of one or both of the drivesignal voltage V_(S) and the drive signal current i_(S).

Likewise in some versions of the invention, the console may include afirst circuit that sets the frequency of the drive signal and a secondcircuit, a variable gain amplifier that sets the potential of the drivesignal. In these versions of the invention, the processor 266

The type of memory device that contains the data describing thecharacteristics of the handpiece and tip that are needed to regulate theoutputting of the drive signal may vary from what has been described.For example, one or more of these memories may be a EEPROM, a bar codeor some other machine readable device. In some versions of theinvention, one or more of the handpiece and tip may not even have amemory. In these versions of the invention, personnel are required tomanually enter the handpiece and tip characteristics into the console inorder to ensure the system 30 is properly configured.

The sequence of steps by which the console 230 sets the potential andfrequency of the drive signal may likewise vary from what has beendescribed. For example, in an alternative configuration of the system,the console may first set the frequency of the drive signal beforesetting the voltage of this signal. Again, depending on the constructionof the invention, the console may not set the frequency and voltage ofdrive signal by setting the corresponding characteristics of a singleWAVEFORM_SET signal. In some versions of the invention, in order toregulate the operation of the components that actual generate the drivesignal, the processing circuit may generate two control signals. A firstone of the control signals is used to set the voltage of the drivesignal. The second control signal is used to set the frequency of thedrive signal.

In the described version of the invention, console 230 is configured toinitially set the drive signal to a frequency that is the lowestpossible longitudinal mechanical cancellation frequency for the tip.Other versions of the invention may be configured to employ analternative frequency as the initial frequency of the drive signal. Forexample, in some version of the invention, the initial frequency of thedrive signal may be the highest possible longitudinal mechanicalcancellation frequency. Alternatively the drive signal may be set afrequency that is between the lowest and highest longitudinal mechanicalcancellation frequencies for the tip. In some versions of the invention,the memory integral with the tip may include data that defines theinitial frequency setting of the longitudinal drive signal.

In the above description, driver capacitance C₀ is assumed to beconstant. This is for the purposes of understanding this invention. Inactuality, driver capacitance may drift over time. This drift can be dueto effects such as aging of the drivers or, during a single procedure, achange in temperature of the drivers. Therefore, some control consolesintegrated into the system of this invention, include a means todetermine driver capacitance. The exact means of making thisdetermination is not part of the invention. From time to time during aprocedure, this means of determining driver capacitance is used toprovide an updated measure of driver capacitance C₀ for use in theevaluations of used to determine the mechanical equivalent of current.

Further the system of this invention may be configured to, based on thepreferences of the practitioner and the specifics of the procedure beingperformed apply a drive signal to the handpiece that causes the tip tovibrate in one of three states. By entering first set of commands intothe console the system would source drive signals to cause the tip tovibrate as described above, substantially torsionally with minimal, ifany, longitudinal vibrations.

By entering a second set of alternative commands into the console 230,the system sources drive signals that cause the tip to vibrate at one ofthe mechanical resonant modes. For the system to operate in this mode,the frequency of the drive signal is set based on the data in fields 194and 195 of the tip memory 184 that define the range of frequencies forthe drive signal when the tip is to be vibrated in the mechanicalresonant mode. When the console is so set it would operate as describedin the incorporated by reference PCT Pub. No. WO 2015/021216 A1. Whenthe system operates in this mode it would be appreciated that distal tothe torsional boundary, the tip shaft 14 and tip head 164 would engagein simultaneous longitudinal and torsional movement. A practitioner maywant the handpiece to operate in this mode if it is believed that thecombined longitudinal and torsional movement of the tip head 164 wouldresult in the optimum removal to tissue and the effects of thelongitudinal motion of the shaft 144 are tolerable.

By entering a third set of commands into the console 230, the systemsources drive signal across the drivers 36 that is a combination of thedrive signals needed to drive the tip at the first resonant mode and thedrive signals needed to drive the tip at the second resonant mode. Whenthe console is so set, the system operates as described in theincorporated by reference PCT App. No. PCT/US2015/044023. A practitionermay want the handpiece to operate in this mode in a situation in whichit is desirable have the tip head 164 engage in non-linear motion inorder to remove tissue and the effects of the longitudinal motion of thetip head are tolerable.

For system 30 to be able to operate in the third mode, the tip memorywould essentially contain two versions of field 194 and two versions offield 195. In the first versions of field 194 and field 195 data arestored that define the range of resonant frequencies of the firstmechanical resonant mode. The second versions of field 194 and 195 dataare stored that define the range of resonant frequencies associated withthe second mechanical resonant mode.

Similarly, by entering a fourth set of commands into the console, thesystem can be set to source a drive signal that is at a frequencybetween the resonant frequency of one of the mechanical resonant modesand the longitudinal mechanical cancelation frequency. Thus, when thesystem is operated in this state, there is a partial cancelation of thelongitudinal motion of the tip head 164 and the adjacent distal section160 of the shaft. This mode of operation may be desirable if, for agiven procedure, it is be appropriate to excite the tip head 164 intovibrations that cause the tip to engage primarily in torsional movementwith some but not the full longitudinal movement.

Additional data that may be stored in the tip memory include datadefining the range of mechanical equivalents of current for each of theresonant modes.

Accordingly, it is the object of the appended claims to cover all suchvariations and modifications that come within the true spirit and scopeof the invention.

What is claimed is:
 1. An ultrasonic tool system comprising: anultrasonic handpiece including: at least one driver that, in response toapplication of an AC drive signal, cyclically expands and contracts, anda tip including opposed proximal and distal ends, the proximal end ofthe tip being coupled to the at least one driver so that the expansionsand contractions of the at least one driver cause longitudinalvibrations at the proximal end of the tip, and a feature between theproximal and distal ends of the tip that converts the longitudinalvibrations present at the proximal end of the tip to vibrations at thedistal end of the tip having a longitudinal component and a torsionalcomponent; and a control console for vibrating the tip of the ultrasonichandpiece, the control console configured to: generate the AC drivesignal that is applied to the at least one driver of the ultrasonichandpiece, the AC drive signal having a variable frequency, and set thefrequency of the AC drive signal so the vibrations at the distal end ofthe tip are substantially torsional.
 2. The ultrasonic tool system ofclaim 1, wherein the control console is configured to set the frequencyof the AC drive signal so the vibrations at the distal end of the tipare substantially torsional by being configured to set the frequency ofthe AC drive signal to a frequency between resonant frequencies of firstand second adjacent mechanical resonant modes of the ultrasonichandpiece, the set frequency corresponding to first vibrations in thetip associated with the first mechanical resonant mode and secondvibrations in the tip associated the second mechanical resonant mode,each of the first and second vibrations having a longitudinal componentand a torsional component, the longitudinal component of the firstvibrations at least partially cancelling out the longitudinal componentof the second vibrations.
 3. The ultrasonic tool system of claim 1,wherein the control console comprises: an assembly for measuring acurrent of the AC drive signal; and an assembly for measuring a voltageof the AC drive signal, wherein the control console is configured to setthe frequency of the AC drive signal so the vibrations at the distal endof the tip are substantially torsional based on the measured current andvoltage.
 4. The ultrasonic tool system of claim 3, wherein the controlconsole is configured to: determine a capacitance of the at least onedriver; and set the frequency of the AC drive signal so the vibrationsat the distal end of the tip are substantially torsional based on themeasured current and voltage and the capacitance of the at least onedriver.
 5. The ultrasonic tool system of claim 4, wherein the controlconsole is configured to: calculate a mechanical equivalent of currentapplied to mechanical components of the ultrasonic handpiece based onthe measured current and voltage, the capacitance of the at least onedriver, and the frequency of the AC drive signal; and set the frequencyof the AC drive signal so the vibrations at the distal end of the tipare substantially torsional based on the mechanical equivalent ofcurrent applied to the mechanical components of the ultrasonichandpiece.
 6. The ultrasonic tool system of claim 5, wherein the controlconsole is configured to calculate a mechanical equivalent of currentapplied to mechanical components of the ultrasonic handpiece based onthe measured current and voltage, the capacitance of the at least onedriver, and the frequency of the AC drive signal by being configured to:calculate a current through the at least one driver based on themeasured voltage, the capacitance of the at least one driver, and thefrequency of the AC drive signal; and determine a difference between themeasured current and the current through the at least one driver.
 7. Theultrasonic tool system of claim 5, wherein the control console isconfigured to: calculate a ratio between current through the at leastone driver to the mechanical equivalent of current applied to themechanical components of the ultrasonic handpiece; and set the frequencyof the AC drive signal so the vibrations at the distal end of the tipare substantially torsional based on the calculated ratio.
 8. Theultrasonic tool system of claim 7, wherein the control console isconfigured to set the frequency of the AC drive signal so the vibrationsat the distal end of the tip are substantially torsional based on thecalculated ratio by being configured to: compare the calculated ratio toa target ratio; and set the frequency of the AC drive signal so thevibrations at the distal end of the tip are substantially torsionalbased on the comparison of the calculated ratio to the target ratio. 9.The ultrasonic tool system of claim 8, wherein the target ratio is zero.10. The ultrasonic tool system of claim 8, wherein the control consoleis configured to compare the calculated ratio to a target ratio by beingconfigured to compare a real component of the calculated ratio to thetarget ratio.
 11. The ultrasonic tool system of claim 4, wherein theultrasonic handpiece comprises a memory storing data indicating thecapacitance of the at least one driver, and the control console isconfigured to determine a capacitance of the at least one driver bybeing configured to read the data indicating the capacitance of the atleast one driver from the memory of the ultrasonic handpiece.
 12. Amethod for controlling an ultrasonic handpiece including at least onedriver that, in response to application of an AC drive signal,cyclically expands and contracts, and a tip including opposed proximaland distal ends, the proximal end of the tip being coupled to the atleast one driver so that the expansions and contractions of the at leastone driver cause longitudinal vibrations at the proximal end of the tip,and a feature between the proximal and distal ends of the tip thatconverts the longitudinal vibrations present at the proximal end of thetip to vibrations at the distal end of the tip having a longitudinalcomponent and a torsional component, the method comprising: generatingthe AC drive signal that is applied to the at least one driver of theultrasonic handpiece, the AC drive signal having a variable frequency,and setting the frequency of the AC drive signal so the vibrations atthe distal end of the tip are substantially torsional.
 13. The method ofclaim 12, wherein setting the frequency of the AC drive signal so thevibrations at the distal end of the tip are substantially torsionalcomprises setting the frequency of the AC drive signal to a frequencybetween resonant frequencies of first and second adjacent mechanicalresonant modes of the ultrasonic handpiece, the set frequencycorresponding to first vibrations in the tip associated with the firstmechanical resonant mode and second vibrations in the tip associatedwith the second mechanical resonant mode, each of the first and secondvibrations having a longitudinal component and a torsional component,the longitudinal component of the first vibrations at least partiallycancelling out the longitudinal component of the second vibrations. 14.The method of claim 12, further comprising: measuring a current and avoltage of the AC drive signal; determining a capacitance of the atleast one driver; and setting the frequency of the AC drive signal sothe vibrations at the distal end of the tip are substantially torsionalbased on the measured current and voltage and the capacitance of the atleast one driver.
 15. The method of claim 14, further comprising:calculating a mechanical equivalent of current applied to mechanicalcomponents of the ultrasonic handpiece based on the measured current andvoltage, the capacitance of the at least one driver, and the frequencyof the AC drive signal; and setting the frequency of the AC drive signalso the vibrations at the distal end of the tip are substantiallytorsional based on the mechanical equivalent of current applied tomechanical components of the ultrasonic handpiece.
 16. The method ofclaim 15, wherein calculating a mechanical equivalent of current appliedto mechanical components of the ultrasonic handpiece based on themeasured current and voltage, the capacitance of the at least onedriver, and the frequency of the AC drive signal comprises: calculatinga current through the at least one driver based on the measured voltage,the capacitance of the at least one driver, and the frequency of the ACdrive signal; and determining a difference between the measured currentand the current through the at least one driver.
 17. The method of claim15, further comprising: calculating a ratio between current through theat least one driver to the mechanical equivalent of current applied tothe mechanical components of the ultrasonic handpiece; and setting thefrequency of the AC drive signal so the vibrations at the distal end ofthe tip are substantially torsional based on the calculated ratio. 18.The method of claim 17, wherein setting the frequency of the AC drivesignal so the vibrations at the distal end of the tip are substantiallytorsional based on the calculated ratio comprises: comparing thecalculated ratio to a target ratio; and setting the frequency of the ACdrive signal so the vibrations at the distal end of the tip aresubstantially torsional based on the comparison of the calculated ratioto the target ratio.
 19. The method of claim 18, wherein comparing thecalculated ratio to a target ratio comprises comparing a real componentof the calculated ratio to the target ratio.
 20. The method of claim 14,wherein the ultrasonic handpiece comprises a memory storing dataindicating the capacitance of the at least one driver, and determining acapacitance of the at least one driver by being comprises reading thedata indicating the capacitance of the at least one driver from thememory of the ultrasonic handpiece.